1. Field of the Invention
The invention relates to an oil additive that can be used in a machine, such as an internal combustion engine, and also relates to an oil filter including the oil additive.
2. Description of Related Art
Various kinds of oil additive agents are put into oil used in a machine, such as an internal combustion engine, so as to curb deterioration of the oil, for example. As one example of the additive agents, zinc dialkyldithiophosphate, or ZnDTP, having an ability to prevent oxidation, an ability to prevent corrosion, an ability to prevent wear, etc., is added to oil.
Japanese Patent Application Publication No. 56-129297 (JP 56-129297 A) discloses the use of a hydrotalcite-like compound expressed in the following formula (1) as an oil additive agent.MgxAl2(OH)6+2x−2y(CO3)y·mH2O   (1)In the above formula (1), x and y are integers that satisfy 3<x<20 and 0<y<2, respectively, and m is an integer. As described in JP 56-129297 A, the hydrotalcite-like compound expressed in the above formula (1) has a characteristic of reacting quickly with undesirable acid pollutants in oil, within the oil, as compared with known basifying agents.
Japanese Patent Application Publication No. 3-296408 (JP 3-296408 A) discloses filter media for a bypass oil filter for an internal combustion engine. The filter media contains the hydrotalcite-like compound expressed in the above formula (1). As described in JP 3-296408 A, fine particles, such as those of the hydrotalcite-like compound, have an acid/alkali adsorption ability, and serve to adsorb acid substances generated in the internal combustion engine, so as to prevent deterioration of oil.
Since the hydrotalcite-like compound has an elution property, the acid substances adsorbed by the hydrotalcite-like compound elute off at the same time as the elution of the hydrotalcite-like compound. The acid substances that elute off again may have adverse influences on the oil. Accordingly, a further development is desired to be made so as to stably curb oil deterioration for a long period of time, using the hydrotalcite-like compound.